Signal processing apparatus and signal processing method

ABSTRACT

An apparatus and a method for allowing a digital broadcast receiver smoothly to switch from one broadcast channel to another. In response to a reproduction output request, encoded data that are requested to be reproduced and output are selected and decoded accordingly. At substantially the same time, arrangements may be provided to select and decode other encoded data in accordance with a predetermined rule. Whenever the encoded data selected using the predetermined rule are to be reproduced and output on request, conventionally required demultiplexing and decoding processes are not needed.

TECHNICAL FIELD

The present invention relates to a signal processing apparatus and asignal processing method for having illustratively an encoded digitalbroadcast signal entered and for decoding the entered signal.

BACKGROUND ART

The start some time ago of digital satellite broadcasting has beenfollowed by widespread acceptance of digital satellite broadcastreceivers by the general public. A large number of broadcast stationsare offering digital satellite broadcast services. The digital satellitebroadcast receiver is typically designed to let any one of multiplechannels be selected from among the numerous offerings.

FIG. 5 is a block diagram outlining an internal structure of aconventional digital satellite broadcast receiver.

As illustrated, the digital satellite broadcast receiver includes afront end section 51, a demultiplexer 52, a decoder 53, and a systemcontroller 50 that controls these components.

The front end section 51 acts on a setting signal supplied from thesystem controller 50, the signal designating transmission specificationsand other technical details. In accordance with the supplied settingsignal, the front end section 51 receives through a parabola antenna(not shown) a carrier (reception frequency) designated by the signal.From the carrier, the front end section 51 acquires a transport stream(TS) through a Viterbi decoding process and an error correction process.

As is well known, the transport stream as per the digital satellitebroadcast criteria is constituted by signal data in compressed form,multiplexed with diverse kinds of additional information. The compresseddata are prepared by compressing video and audio signals of a pluralityof broadcast programs in accordance with MPEG-2 (Moving Picture ExpertsGroup Layer 2). The additional information, to be inserted by broadcaststations, includes PSI (program specific information) accommodatingtables such as PAT (program association table) and PMT (program maptable), and SI (service information, serving as program scheduleinformation).

The front end section 51 obtains PSI (program specific information)packets from the transport stream (TS) in order to update channel selectinformation. From the transport stream, the front end section 51 alsoacquires a component PID (program ID) on each of the available channelsand forwards the acquired component PID's illustratively to the systemcontroller 50. The system controller 50 utilizes the received PID's inprocessing the received signals.

In keeping with a filtering condition established by the systemcontroller 50, the demultiplexer 52 filters out necessary TS packetsfrom the transport stream supplied by the front end section 51, in amanner to be described later. Illustratively, the demultiplexer 52obtains regarding a target broadcast program two kinds of TS packets: TSpackets of video data compressed in the MPEG-2 format, and TS packets ofaudio data compressed also in the MPEG-2 format. The compressed videoand audio data thus acquired are output to the decoder 53.

The decoder 53 is made up of a video decoder and an audio decoder. Thevideo decoder decodes compressed video data in accordance with theMPEG-2 format for output. The audio decoder decodes compressed audiodata in keeping with the MPEG-2 format and outputs the decoded audiodata in synchronism with the video data output. The compressed video andaudio data that have been input are thus decoded by the video decoderand audio decoder respectively.

The video and audio data that have been decoded and synchronized asoutlined above are output for reproduction purposes by the decoder 53.

In operation, the conventional digital satellite broadcast receiver ofthe above-described structure may receive a channel select request froma user manipulating the receiver. In such a case, the steps outlinedbelow are typically carried out.

FIG. 6 is a flowchart of steps in which the conventional digitalsatellite broadcast receiver selects a channel.

In step S1001, the system controller 50 of the receiver checkscontinuously whether a channel select request is made. If the channelselect request is found to be made, the system controller 50 goes tostep S1002 and recognizes the channel number of the requested channel.

In step S1003, NIT (network information table) is received on the basisof PAT (program association table). As is well known, NIT includeschannel-related physical characteristic information (e.g., satelliteorbit data, polarized waves, and frequency of each of the transpondersassociated with digital satellite broadcasts). The received NIT is usedin step S1003 as a basis for recognizing the transponder frequencycovering the requested channel.

In step S1003, the frequency thus recognized is set anew for the frontend section 51. This causes the front end section 51 to receive thetransponder frequency covering the requested channel.

In step S1004, PAT is acquired from the transponder frequency receivedanew by the front end section 51. In step S1005, PMT of the requestedchannel is received in accordance with information in the newly-receivedPAT.

In step S1006, a filtering condition is set for the demultiplexer 52based on PMT. The condition allows the demultiplexer 52 to filter outonly the packets of the requested channel from the transport stream ofthe transponder, whereby stream data are obtained.

In step S1007, SH (sequence header) is detected from the stream dataacquired by the demultiplexer 52 in the manner described above. From thedetected SH, the demultiplexer 52 recognizes a video format (e.g.,standard definition (SD) or high definition (HD)) of the stream data onthe requested channel.

In step S1008, SH detected in step S1007 is used as a basis forestablishing various settings needed by the decoder 53 to operate inkeeping with the relevant format.

In step S1009, the decoder 53 is prompted to execute a decoding processbased on the settings. The decoder 53 thereby establishessynchronization between video data and audio data.

In step S1010, the decoder 53 is prompted to output the video and audiodata thus prepared. This is how the audio and video data from thechannel requested in step S1001 are output.

As described, the conventional digital satellite broadcast receiverperforms two stages of processing, i.e., demultiplexing (steps S1002through S1006 in FIG. 6) and decoding (steps S1007 through S1009), fromthe time a channel select request is made until an image of therequested channel is displayed.

As can be seen from the foregoing description, the demultiplexingprocess can take long, as much as hundreds of milliseconds. That isbecause the process involves carrying out a fairly large number of stepsin sending and receiving various signals. Likewise, the decoding processcan take hundreds of milliseconds because it is relatively complicatedin execution.

As a result, the conventional digital satellite broadcast receiver cantake up to one second between the channel select request and the outputof video display. This amounts to a substantially long delay in channelselection compared with the typical analog TV set (television receiver)receiving analog broadcasts.

With such behavior, many conventional digital satellite broadcastreceivers have often aroused in their users a feeling of awkwardness dueto the prolonged channel select time that is considerably longer thanthat of analog TV sets.

DISCLOSURE OF INVENTION

The present invention has been made in view of the above circumstancesand provides a signal processing apparatus that is structured asoutlined below.

According to one aspect of the invention, there is provided a signalprocessing apparatus comprising: an inputting means for inputting adesignated plurality of encoded data; an encoded data selecting meansfor selectively outputting a designated plurality of encoded data from aplurality of encoded data which have been input by the inputting means;and a plurality of decoding means for individually inputting theplurality of encoded data selected by the encoded data selecting meanswhile decoding the encoded data which have been input.

The signal processing apparatus further comprises: an encoded datadesignating means for designating encoded data for the inputting meansand for the encoded data selecting means in such a manner that inresponse to a reproduction output request, the encoded data requested tobe reproduced and output and other encoded data which are selected inaccordance with a predetermined rule and which differ from the encodeddata requested to be reproduced and output are input individually to theplurality of decoding means; and a reproduction output controlling meansfor controlling the plurality of decoding means to output only theencoded data requested to be reproduced and output following thedecoding in response to the reproduction output request.

When the above structure is in place, the encoded data designating meansspecifies that one of the decoding means is to decode the encoded datarequested to be reproduced and output. Concurrently, the encoded datadesignating means specifies that another decoding means is to decodeother encoded data which differ from the encoded data to be reproducedand output and which are selected in accordance with a predeterminedrule.

If the reproduction output request is made for the encoded data selectedin keeping with the predetermined rule, then the reproduction outputcontrolling means permits output of the encoded data in question whichhave been decoded beforehand as described.

Where the encoded data selected in accordance with the predeterminedrule are decoded in advance, the reproduction output request made forthe encoded data in question causes the data to be reproduced and outputwithout the need for the selecting process by the encoded data selectingmeans, for the designating process by the encoded data designatingmeans, and for the decoding process by the decoding means.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a principal internal structure of adigital broadcast receiver 1 practiced as an embodiment of thisinvention;

FIG. 2 is a flowchart of steps constituting a channel selection processperformed by the digital broadcast receiver 1 as the embodiment of theinvention;

FIG. 3 is a flowchart of steps constituting a predecoded channel settingprocess carried out by the embodiment;

FIG. 4 is a flowchart of steps constituting another predecoded channelsetting process executed by the embodiment;

FIG. 5 is a schematic block diagram outlining a typical structure of aconventional digital satellite broadcast receiver; and

FIG. 6 is a flowchart of steps constituting a channel selection processperformed by the conventional digital satellite broadcast receiver.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a block diagram showing a principal internal structure of thedigital broadcast receiver 1 to which a signal processing circuitembodying this invention is applied. As illustrated, the digitalbroadcast receiver 1 has a dual-tuner pack structure including a firstfront end section 4 a and a second front end section 4 b.

The digital broadcast receiver 1 also includes, as shown, a third frontend section 4 c that acts as a tuner pack for addressing terrestrialdigital broadcasts. The multiple front end sections 4 thus furnishedallow the digital broadcast receiver 1 to admit a plurality oftransponder frequencies simultaneously.

The first front end section 4 a and second front end section 4 b areconnected to a BS parabola antenna 2 a and a CS parabola antenna 2 b setup outside an enclosure of the digital broadcast receiver 1. The twoparabola antennas 2 a and 2 b receive broadcast signals via satelliteand have them converted into predetermined high-frequency signals usingbuilt-in low noise block down converters (LNB). The high-frequencysignals are forward as the received signals through a mixer 15 (shown)to the first and the second front end sections 4 a and 4 b.

Likewise, the third front end section 4 c is connected to a terrestrialwave antenna 3 that receives terrestrial digital broadcast signals. Thereceived signals are fed to the third front end section 4 c.

The first, the second and the third front end sections 4 a, 4 b and 4 coperate on a setting signal supplied by a system controller 10, thesetting signal designating transmission-related specifications and otherrelevant details. Given the setting signal, the front end sectionsaccordingly receive transponder (carrier) frequencies that are subjectedto Viterbi decoding and error correction, whereby a transport stream(TS) is obtained.

As is well known, the transport stream as per digital satellitebroadcast criteria has compressed data multiplexed with diverse kinds ofadditional information. The compressed data are prepared by compressingvideo and audio signals of a plurality of broadcast programsillustratively in accordance with MPEG-2 (Moving Picture Experts GroupLayer 2) standards.

The compressed data made up of the video and audio signals aremultiplexed into an elementary stream (ES). The additional informationto be inserted by broadcast stations includes PSI (program specificinformation) including tables such as PAT (program association table)and PMT (program map table), and SI (service information, serving asprogram schedule information).

The multiplexing of the information above is accomplished as follows:the transport stream is first formed with 188-byte transport streampackets (TS packets). The elementary stream (ES) described above and thediverse kinds of additional information are then placed into the TSpackets to constitute the transport stream in its multiplexed form.

Each of the first through the third front end sections 4 a through 4 cacquires PSI (program specific information) packets from the transportstream in order to update channel select information. At the same time,each front end section obtains from the transport stream a component PID(program ID) on each of the available channels and forwards the acquiredcomponent PID's illustratively to the system controller 10. The systemcontroller 10 utilizes the received PID's in processing the receivedsignals.

In keeping with a filtering condition established by the systemcontroller 10, a demultiplexer 5 filters out necessary TS packets fromthe transport stream supplied by the front end sections 4.Illustratively, the demultiplexer 5 obtains regarding a target broadcastprogram two kinds of TS packets: TS packets of video data compressed inthe MPEG-2 format, and TS packets of audio data compressed also in theMPEG-2 format.

Under control of the system controller 10, the demultiplexer 5 outputsthe compressed video and audio data thus acquired to a first decoder 6a, a second decoder 6 b and a third decoder 6 c (to be described later)in matrix fashion. More specifically, the transport stream acquired fromthe first front end section 4 a may be output to the third decoder 6 c,the TS from the second front end section 4 b to the first decoder 6 a,and the TS from the third front end section 4 c to the second decoder 6b.

The individual packets of the compressed video/audio data filtered outby the demultiplexer 5 are input to the first decoder 6 a, seconddecoder 6 b, and third decoder 6 c in PES (packetized elementary stream)form.

The filtering condition is established as follows: the demultiplexer 5first extracts PAT, PMT, etc., from the transport stream and transfersthe extracted tables to the system controller 10. In turn, the systemcontroller 10 sets the filtering condition for the demultiplexer 5 onthe basis of the specifics described in the transferred tables.

The first, the second and the third decoders 6 a, 6 b and 6 c are eachmade up of a video decoder and an audio decoder. The video decoderdecodes input compressed video data in accordance with the MPEG-2format. The audio decoder decodes input compressed audio data in keepingwith the MPEG-2 format. The compressed video and audio data that havebeen input are thus decoded by the video decoder and audio decoderrespectively.

Each of the first, the second and the third decoders 6 a, 6 b and 6 csynchronizes the decoded video and audio data based on PTS (presentationtime stamp, serving as output time management information) that has beenmultiplexed with the broadcast signals and which is supplied by thedemultiplexer 5. The video and audio data thus synchronized are fed toan output switch section 7 as illustrated.

As described above, the digital broadcast receiver 1 embodying thisinvention includes three decoders, i.e., the first, the second and thethird decoders 6 a, 6 b and 6 c. This multiple decoder arrangementallows stream data on a plurality of channels to be decodedsimultaneously.

For example, the first decoder 6 a may be arranged to decode the data onthe currently-selected broadcast channel as will be discussed later. Thesecond decoder 6 b and third decoder 6 c may predecode the data on otherchannels that are set according to a predetermined rule.

In this description, all decoding over the channels that are differentfrom the currently-selected channel is referred to as predecoding.

Under control of the system controller 10, the output switch section 7switches the output of the video and audio data coming from the firstthrough the third decoders 6 a through 6 c. In this manner, the outputswitch section 7 outputs the audio and video data requested to bereproduced and output on one channel at a time, as illustrated.

An operation input section 8 is constituted by a plurality of operatingelements, not shown, furnished outside the enclosure of the digitalbroadcast receiver 1. The operating elements illustratively include:channel select keys for selecting a desired channel from receivedbroadcast signals (i.e., keys for making a channel select request);successive channel select keys for successively selecting channelnumbers; and direct channel select keys for directly selecting each ofthe available channels. Also included are broadcast select keys forselecting any one of the BS, CS, and terrestrial broadcasts.

The operation input section 8 of the above constitution is arranged tosupply the system controller 10 with operation signals representative ofthe operating elements being operated on. The system controller 10carries out its processing based on the supplied operation signals.

A remote commander signal reception section 9 receives command signalsillustratively in infrared rays from a remote commander 9 a shown inFIG. 1. In turn, the remote commander signal reception section 9supplies the system controller 10 with operation signals representingthe received command signals. As is the case with the operation inputsection 8, the system controller 10 performs its processing on the basisof the supplied operation signals.

It is assumed that the remote commander 9 a at least has operatingelements for permitting the operations equivalent to those made on theabove-mentioned operation input section 8.

A RAM 12 is furnished to act as a work area for use by the systemcontroller 10. The system controller 10 writes and reads data to andfrom the RAM 12 as needed.

A ROM 11 is a nonvolatile memory such as a flash memory. The ROM 11contains programs that allow the system controller 10 to provide overallcontrol on all configured devices. The system controller 10 performs itsoperations in keeping with these programs.

The ROM 11 also contains a program that permits the setting ofpredecoded channels and the execution of channel select operations. Thesystem controller 10 operating in accordance with this program allowsthe digital broadcast receiver 1 to implement a channel select operationand a predecoded channel setting operation, to be described later.

For the inventive digital broadcast receiver 1 structured as describedabove, it is assumed that the channel number immediately preceding thecurrently-selected channel number and the channel number immediatelyfollowing it are selected as the predecoded channels. That assumption ispredicated on another assumption: that the channel select operation isperformed by the user most often operating the successive channel selectkeys.

That is, the channels likely to be selected by operation of thefrequently-used channel select keys are set to be predecoded at alltimes. This leads to an enhanced possibility that one of the predecodedchannels will be selected next.

For example, suppose that the currently-selected channel number is 100.In that case, the digital broadcast receiver 1 of this embodiment worksillustratively as follows:

Where the transport stream containing the stream data on channel No. 100is being acquired by the first front end section 4 a, the transportstream including the stream data on the immediately-preceding channelNo. 99 may be obtained by the second front end section 4 b, and thetransport stream including the stream data on the immediately-followingchannel No. 101 may be gained by the third front end section 4 c.

Where the demultiplexer 5 feeds the transport stream of channel No. 100to the first decoder 6 a for decoding, the transport stream of channelNo. 99 and that of channel No. 101 may be fed by the demultiplexer 5 tothe second decoder 6 b and third decoder 6 c for predecoding,respectively.

In the case above, the output switch section 7 connects its outputswitch to the first decoder 6 a decoding the currently-selected channelNo. 100. This allows the data on channel No. 100 alone to be output.

Suppose now that the user selects channel No. 101 by operating on thesuccessive channel select keys. The channel select operation causes theoutput switch section 7 to connect its output switch to the thirddecoder 6 c decoding channel No. 101. This allows the data on channelNo. 101 to be reproduced and output.

That is, the channel select operation leads directly to the switching ofthe output switch section 7, and the data on the newly-selected channelcan be reproduced and output immediately.

In parallel with the reproduction and output of channel No. 101, thechannel select operation initiates the setting of new channels to bepredecoded, i.e., channel No. 100 immediately preceding thecurrently-selected channel No. 101 and channel No. 102 immediatelyfollowing it.

FIG. 2 is a flowchart of steps constituting such a channel selectionprocess performed by this embodiment of the invention. In step S101 ofFIG. 2, the system controller 10 checks continuously whether a channelselect request (i.e., reproduction output request) is made,illustratively by the user performing a channel select operation on theoperation input section 8 or on the remote commander 9 a. If the channelselect request is recognized, step S102 is reached.

In step S102, the system controller 10 checks whether the channeldesignated by the channel select request (called the requested channelhereunder) is a predecoded channel.

In practice, after the channel select request is detected in step S101,the check in step S102 is carried out in parallel with theabove-described process in which the channel number immediatelypreceding the requested channel and the channel number immediatelyfollowing it are established as predecoded channels.

With this digital broadcast receiver 1, each of the predecoded channelsthus established is subject to demultiplexing (steps S105 through 108,to be described later) and decoding (steps S109 through S112, to bediscussed later) in parallel with the reproduction and output of what isbeing broadcast on the requested channel.

If the requested channel is not found to be a predecoded channel in stepS102, then step S105 is reached. From step S105 on, demultiplexing anddecoding are carried out as described below. That is, the sameprocessing as the conventional set of channel select operations isexecuted.

In step S105, NIT (network information table) is received on the basisof the above-described PAT. As is well known, NIT includeschannel-related physical characteristic information (e.g., satelliteorbit data, polarized waves, and frequency of each of the transpondersassociated with digital satellite broadcasts). The received NIT is usedin step S105 as a basis for recognizing the transponder frequencycovering the requested channel.

In step S105, the frequency thus recognized is set anew for any one ofthe front end sections 4. This causes the front end section 4 inquestion to receive the transponder frequency covering the requestedchannel.

In step S106, PAT is acquired from the transponder frequency receivedanew by the front end section 4. In step S107, PMT of the requestedchannel is received in accordance with information in the newly-receivedPAT.

In step S108, a filtering condition is set for the demultiplexer 5 basedon PMT. The condition allows the demultiplexer 5 to filter out only thepackets of the requested channel from the transport stream of thetransponder, whereby stream data are obtained.

In step S109, SH (sequence header) is detected from the stream dataacquired by the demultiplexer 5 in the manner described above. From thedetected SH, the demultiplexer 5 recognizes a video format of compressedvideo data (e.g., standard definition (SD) or high definition (HD)) ofthe stream data on the requested channel.

In step S110, SH detected in step S109 is used as a basis forestablishing various settings needed by any one of the decoders 6 tooperate in keeping with the relevant format.

More specifically, executing step S110 involves selecting one of thedecoders 6 by which to decode the stream data on the requested channeland making the necessary settings for the selected decoder 6. Then thedemultiplexer 5 is arranged to supply the stream data to the selecteddecoder 6.

In step S111, the decoder 6 for which the settings have been made isprompted to execute a decoding process based on the settings. Thedecoder 6 thereby establishes synchronization between video data andaudio data.

In step S112, the output switch section 7 is arranged to switch to thedecoder 6 currently decoding the requested channel. In step S113, theoutput switch section 7 outputs the video and audio data on therequested channel.

If the check in step S102 reveals that the requested channel is apredecoded channel, then step S103 is reached. As discussed above, thestream data on each predecoded channel have already undergone thedemultiplexing and decoding processes. The decoder 6 that is currentlydecoding is thus recognized in step S103, and the output switch section7 is connected to the output of the recognized decoder in step S104.

In the manner described above, when a predecoded channel is requested bythe channel select request, the digital broadcast receiver 1 of thisembodiment can skip the demultiplexing and decoding processes carriedout conventionally when a new channel is to be selected. In other words,what is being broadcast on the selected channel can be reproduced andoutput immediately after the operation to select that channel isexecuted.

The example explained above in connection with FIG. 2 involved settingas predecoded channels the channel number immediately preceding thecurrently-selected channel number and the channel number immediatelyfollowing it. This scheme is effective when the successive channelselect keys are operated to select one of the two predecoded channels,but not when the direct channel select keys are operated to select achannel number other than the two channels.

In order to deal with such an eventuality, this embodiment of theinvention permits predecoding of the channels in descending order oftheir past select counts each representing the number of times a givenchannel has been selected so far.

FIG. 3 is a flowchart of steps constituting the predecoded channelsetting process in which the system controller 10 sets predecodedchannels in descending order of the past select counts of the availablechannels.

The processing in FIG. 3 proceeds in parallel with the processing inFIG. 2, as in the above-described case in which the channel numberimmediately preceding the currently-selected channel and the channelnumber immediately following it are set as predecoded channels.

In step S201 of FIG. 3, a check is thus made continuously to see whethera channel select request is made. When the channel select request isdetected, step S202 is reached. In step S202, the channel number of therequested channel is recognized.

In step S203, on the basis of the recognition in step S202, a relevantchannel request count stored in correspondence with each of theavailable channels is updated.

More specifically, a predetermined area in the RAM 12 may be set asideto retain a table of the channels each associated with the number oftimes the channel in question has been requested in the past. When achannel select request is recognized, the request count datacorresponding to the requested channel are updated in the table, wherebythe select request count of each channel is properly managed.

In the manner described, the select request count data regarding therequested channel are updated in step S203. Step S203 is followed bystep S204.

In step S204, the channels are ranked in descending order of theirselect request counts written in the table. In step S205, the first- andthe second-ranked channels are illustratively set as predecoded channelsbased on the ranking determined in step S204.

When the processing of FIG. 3 is carried out as described, top-rankedchannels are selected as predecoded channels in descending order of thepast select counts of the available channels. The larger the number oftimes a given channel has been selected in the past, the more likelythat channel will be selected by this digital broadcast receiver 1 asone of the predecoded channels.

It follows that with the processing of FIG. 3 executed, a channel selectrequest issued illustratively by operation of the direct channel selectkeys is efficiently dealt with by this embodiment taking advantage ofthe effectiveness of its predecoded channel setting process.

As another example, it is also possible to set as predecoded channelstop-ranked channels in descending order of channel select times eachrepresenting the length of time required to select each of the availablechannels. More specifically, on each of the available channels, a timeperiod is measured starting from the time a channel select request ismade until images of the requested channel are output. The longer thetime it takes to output the video of a given channel, the higher thechannel is ranked to be set as one of the predecoded channels.

FIG. 4 is a flowchart of steps performed by the system controller 10selecting predecoded channels in descending order of the channel selecttimes measured. The processing in FIG. 4 also proceeds in parallel withthe processing in FIG. 2.

In step S301 of FIG. 4, a check is made continuously to see whether achannel select request is made. If the channel select request isrecognized, step S302 is reached in which a check is made to see if therequested channel is a predecoded channel.

If the requested channel is found to be a predecoded channel, theroutine of FIG. 4 is executed. No subsequent steps are then carried outto measure a channel select time. That is, step S302 is inserted here toprevent the steps that follow from getting executed wastefully tomeasure the channel select time for any channel having been predecoded.

If in step S302 the requested channel is not found to be a predecodedchannel, step S303 is reached. In step S303, the time required to selectthe requested channel is measured.

In step S304, the channel select time thus measured is written to atable of channel select times. In this case, too, a predetermined areain the RAM 12 may be set aside to retain the table of channel selecttimes each representing the length of time required to select each ofthe available channels. The channel select time measured in step S303 iswritten to this table.

In step S305, the channels are ranked in descending order of theirselect time by referring to the table of channel select times. In stepS306, the first- and the second-ranked channels are illustratively setas predecoded channels based on the ranking determined in step S306.

When the processing of FIG. 4 is carried out as described, top-rankedchannels are selected as predecoded channels in descending order of thepast channel select times of the available channels. The longer the timeperiod required to select a given channel in the past, the more likelythat channel will be selected by this digital broadcast receiver 1 asone of the predecoded channels.

In the majority of cases, viewers of digital BS and CS broadcasts tendto view a relatively limited group of channels. Of such limitedchannels, those that it particularly takes time to select can thus beestablished preferentially as predecoded channels.

With the processing of FIG. 4 executed, it is possible to eliminate thepresence of those channels which, when selected, arouse in viewers asense of awkwardness because of the prolonged channel select time fromthe time a channel select request is made until images of the requestedchannel are output.

As described above, the digital broadcast receiver 1 embodying thisinvention includes a plurality of decoders, i.e., the first, the secondand the third decoders 6 a, 6 b and 6 c. One of the decoders decodes theselected channel (requested channel) and outputs the decoded result.

In parallel with the decoding process, the other decoders are arrangedto predecode other channels than the requested channel. If any of thepredecoded channels is selected by a channel select request, theinventive arrangement connects the output switch section 7 to thecorresponding decoder that is predecoding, whereby the audio and videodata on the requested channel are output.

That is, whenever switching to one of the predecoded channels, thedigital broadcast receiver 1 of this embodiment can skip thedemultiplexing and decoding processes conventionally required whenpredecoding is not implemented.

For this embodiment, the predecoded channels were shown to be set in oneof three cases: the channel number immediately preceding thecurrently-selected channel and the channel number immediately followingit are set as predecoded channels; top-ranked channels in descendingorder of the channel request counts of the available channels are set aspredecoded channels; or top-ranked channels in descending order of thechannel select times of the available channels are set as predecodedchannels. However, these cases each presented as the rule by which toset predecoded channels are only examples and are not limitative of theinvention.

Obviously, the number of predecoded channels is not limited to two.Three or more channels may be predecoded.

As another example, EPG (electronic program guide) multiplexed ondigital broadcast signals may be utilized as a basis for settingpredecoded channels. The predecoded channels in this case may be setillustratively as follows:

The program information included in EPG on the broadcast signals isreferenced over time. This makes it possible to recognize and retain thename of, for example, the genre of broadcast programs most often watchedby the user in the past. The channels carrying EPG describing the genrename thus recognized are established as predecoded channels.

As another alternative, information about the cast of themost-often-watched broadcast programs may be found out, and predecodedchannels may be established accordingly. In this case, the user'spreferences are reflected in the setting of the predecoded channels.This feature is convenient for users who frequently watch a specificgenre of broadcast programs.

Although the signal processing apparatus according to the invention wasshown applied to the digital broadcast receiver 1 of this embodiment,this is not limitative of the invention. Alternatively, the inventivesignal processing apparatus may be applied advantageously to hard discdrive (HDD) recorders or like equipment allowing any one of a pluralityof streams of encoded data to be selectively decoded and output.

In a typical HDD recorder, a plurality of transport streams (TS) areinput to its HDD equivalent to the front end section 51 of FIG. 5.Conventionally, of the multiple transport streams stored on the HDD, therequested TS is selectively reproduced and output through demultiplexingand decoding.

When the signal processing apparatus of this invention is applied to theexample above, a plurality of decoders are installed so that some ofthem may receive from the HDD the transport streams determinedpreferentially by a predetermined rule for predecoding purposes. Thescheme makes it possible immediately to output and display any one ofthe predecoded transport streams which is currently requested by thechannel selected request.

The signal processing apparatus of this invention may also be applied toso-called Internet radio equipment for reproducing and outputting thedata broadcast by Internet radio stations. Such equipment is typicallyarranged to buffer a predetermined quantity of data from each selectedbroadcast channel. Every time a new channel is selected, it takes sometime for the data on that channel to be reproduced and output.

When the inventive signal processing apparatus is applied to the aboveequipment, the data on preselected channels other than thecurrently-reproduced channel may be buffered and decoded in advance.This arrangement makes it possible to reduce significantly the length oftime from the time a channel select request is issued until the data onthe requested channel are reproduced and output.

Although the inventive signal processing apparatus was shown applied tothe digital broadcast receiver 1 of this embodiment in which thedecoders 6 are designed to comply with the MPEG-2 standard, this is notlimitative of the invention. Alternatively, the decoders 6 may bearranged to comply with other video compression methods. Furthermore,the decoders may also comply with such audio compression methods as WMA(Windows (registered trademark) Media Audio) and ATRAC-3 (AdaptiveTRansform Acoustic Coding Version 3).

Although the embodiment above was presented using examples in which thesignal processing apparatus is implemented as part of hardware, this isnot limitative of the invention. Alternatively, the signal processingapparatus may be implemented on a software basis.

In addition, although this embodiment was shown having the first, thesecond and the third decoders 6 a, 6 b and 6 c implemented asindependent pieces of hardware, this is not limitative of the invention.Alternatively, a single decoder of relatively high performance may bearranged to execute the functions of the multiple decoders 6 on atime-shared basis. The effect of the alternative setup is still thesame.

INDUSTRIAL APPLICABILITY

As described, the signal processing apparatus according to thisinvention permits decoding of encoded data requested to be reproducedand output by use of a reproduction output request. Concurrently, thesignal processing apparatus predecodes encoded data that are selected inkeeping with a predetermined rule.

If a new reproduction output request is made for the encoded datapreselected as per the predetermined rule, the data need only be outputwith no further intervention because they have been predecoded.

That is, when the encoded data selected in accordance with thepredetermined rule are to be reproduced and output, the inventiveapparatus has no need for the demultiplexing and decoding processes thatare required conventionally upon switchover to newly-selected data.

As a result, the signal processing apparatus of this inventiondrastically reduces the time that elapses from the time a reproductionoutput request is made until the encoded data requested thereby areoutput. The user operating the digital broadcast receiver is thus ableto make smoothly-executed channel select operations.

1. A signal processing apparatus comprising: inputting means forinputting a designated plurality of encoded data; encoded data selectingmeans for selectively outputting a designated plurality of encoded datafrom a plurality of encoded data which have been input by said inputtingmeans; a plurality of decoding means for individually inputting theplurality of encoded data selected by said encoded data selecting meanswhile decoding the encoded data which have been input; encoded datadesignating means for designating encoded data for said inputting meansand for said encoded data selecting means in such a manner that inresponse to a reproduction output request, the encoded data requested tobe reproduced and output and other encoded data which are selected inaccordance with a predetermined rule and which differ from said encodeddata requested to be reproduced and output are input individually tosaid plurality of decoding means for predecoding; and reproductionoutput controlling means for controlling said plurality of decodingmeans to output said encoded data requested to be reproduced and outputfollowing the decoding in response to said reproduction output request,wherein said predetermined rule stipulates that said plurality ofencoded data, which have been input by said inputting means, are rankedin terms of a channel select time which is a time period measured fromthe time a request to select a channel corresponding to the requestedencoded data is made until the requested encoded data are output, andthat top-ranked encoded data are selected in descending order of thechannel select times.
 2. The signal processing apparatus according toclaim 1, wherein said predetermined rule stipulates that, of theplurality of encoded data which have been input and acquired by saidinputting means receiving digital broadcasts, the encoded datacorresponding to a broadcast channel number either preceding orfollowing the broadcast channel number representing said encoded datarequested to be reproduced and output are selected.
 3. The signalprocessing apparatus according to claim 1, wherein said predeterminedrule stipulates that said plurality of encoded data which have beeninput by said inputting means be ranked in terms of a reproductionoutput request count representing the number of times said reproductionoutput request is made for specific encoded data, and that top-rankedencoded data are selected in descending order of the reproduction outputrequest counts.
 4. The signal processing apparatus according to claim 1,wherein said predetermined rule stipulates that the encoded data beselected which are determined on the basis of information which ismultiplexed on broadcast signals input by said inputting means and whichindicates broadcast genres.
 5. A signal processing method comprising thesteps of: inputting by an inputting means, a designated plurality ofencoded data; selectively outputting a designated plurality of encodeddata from a plurality of encoded data that have been input; individuallyinputting the selected plurality of encoded data while decoding theencoded data which have been input; designating encoded data for saidinputting step and for said encoded data selecting step in such a mannerthat in response to a reproduction output request, the encoded datarequested to be reproduced and output and other encoded data which areselected in accordance with a predetermined rule and which differ fromsaid encoded data requested to be reproduced and output are inputindividually for predecoding; and outputting said encoded data requestedto be reproduced and output following the decoding in response to saidreproduction output request, wherein said predetermined rule stipulatesthat said plurality of encoded data, which have been input by saidinputting means, are ranked in terms of a channel select time which is atime period measured from the time a request to select a channelcorresponding to the requested encoded data is made until the requestedencoded data are output, and that top-ranked encoded data are selectedin descending order of the channel select times.
 6. The signalprocessing method according to claim 5, wherein said predetermined rulestipulates that, of the plurality of encoded data which have been inputand acquired through reception of digital broadcasts, the encoded datacorresponding to a broadcast channel number either preceding orfollowing the broadcast channel number representing said encoded datarequested to be reproduced and output are selected.
 7. The signalprocessing method according to claim 5, wherein said predetermined rulestipulates that said plurality of encoded data which have been input beranked in terms of a reproduction output request count representing thenumber of times said reproduction output request is made for specificencoded data, and that top-ranked encoded data are selected indescending order of the reproduction output request counts.
 8. Thesignal processing method according to claim 5, wherein saidpredetermined rule stipulates that the encoded data be selected whichare determined on the basis of information which is multiplexed on inputbroadcast signals and which indicates broadcast genres.